I think think that the biggest challenge of going from the floor to the ED is the change of mindset and focus of care. Essentially you will have to unlearn what you knew about nursing on the floor and develop new habits which takes time.
First, Prioritize. When you take over a zone, who is your sickest patient? What needs to be done to get your patients home or to the floor? Our job is to rule out the worst case scenario based on the patients presenting and current symptoms. We don't care if your stomach hurt once two weeks ago. We care if it hurts now. Your challenge is to anticipate what they will need and to identify your most critical patients. Sometimes it's not always obvious. Know the plan of care or what you are trying to rule out for each patient.
Ask questions. It's always better to ask the question and feel stupid if you have any doubt then not ask the question. Show interest and get involved. If there's a code, get in there or atleast observe. Ask if there is anything you can help with. We notice that. Have a sense of urgency when appropriate.
There is so much more but you will learn. Good luck!